This invention relates generally to the drying of coated webs and, more particularly, to improvements in a microwave applicator of the serpentine type.
It is known in the art that amorphous polymeric webs can be coated with an aqueous dispersion and dried before being biaxially stretched or drawn. According to the disclosure of Pears in Br. 1,411,564, drying may be effected in a hot air oven.
It is also known in the art that various objects can be treated with microwave energy. For example, a serpentine applicator for heating thin sheets of moistened paper is disclosed in U.S. Pat. No. 3,47l,672 to White. The applicator has coupling holes between successive waveguides. A particular load can be matched to the source of microwave energy by an adjustment of shorting plates at the ends of the waveguides. However, such an applicator does not remain tuned with varying loads, for example, in the drying of aqueous coatings on wide polymeric webs of different gauges and widths, all of which can be processed at different speeds and receive coatings with different weights and concentrations of additives.